Soil aggregation and surface-soil properties under grazed pastures and other conservation land uses in Virginia

Abstract

Grazed pastures supporting ruminant livestock have not been well characterized for soil health condition. However, growing interest in holistic management of compromised watersheds suggests that grazing lands deserve more attention for their capacity to provide ecosystem services. Relatively little is known about how grazing management affects soil aggregation and other surface-soil properties on private lands in the eastern United States. This study investigated the effects of land use (conventional-till cropland, no-till cropland, grassland, and woodland) and pasture management characteristics on soil aggregation, bulk density, sieved soil density, total soil N, and soil-test biological activity on 31 private farms distributed across the western half of Virginia. Soil stability index followed the order (p < 0.05): conventional-till cropland (0.60 mm mm⁻¹) < no-till cropland (0.78 mm mm⁻¹) < woodland (0.85 mm mm⁻¹) = grassland (0.89 mm mm⁻¹). Surface soil characteristics improved with pasture age due to organic matter recycling from residual forage mass and animal excreta. Increases in total soil N and soil-test biological activity helped create water-stable aggregation and reduce soil bulk density. Soil stability index was optimized with moderate stocking rate of 0.5–1.1 Mg live weight ha⁻¹. Stocking method did not affect soil aggregation or bulk density. Soil stability index declined with increasing N fertilization rate. Soil aggregation characteristics were generally not affected by organic amendment, quantity of hay fed on farm, or occasional hay harvest from pastures, likely because aggregation was high across management variables. Well-managed grazed pastures in Virginia are creating desirable conservation agricultural land uses to protect watershed quality.